Basically it calls on Havant Borough Council to fund more and better information on sewage discharges into the harbours for water users such as rowers, paddle-boarders, etc. While this won't solve the problem, it will raise awareness and therefore pressure on Southern Water to stop / sharply curtail its discharges into the harbours.
Re: Sewage in Chichester and Langstone Harbours - Petition
One more thing. I followed up to check out Southern Water's BeachBuoy system, which is how they report releases of untreated sewage from Combined Sewer Overflows. Here's a link to their site. You will see that they report information about the Chichester Harbour, Langstone Harbour and other locations near us. I looked through them and, surprise, surprise, there was a release of untreated sewage into the Langstone Harbour around 13th March, see the yellow marking on this picture. I'm not sure how serious it was, but all this underlines the need for better information, etc.